AcrIF1 (also known as AcrF1) is an anti-CRISPR (Acr) protein that targets type I-F Csy and blocks CRISPR-RNA (crRNA) and invader DNA hybridization. It has been shown that multiple copies of AcrIF1 bind to the CRISPR-Cas (Clustered Regularly Interspaced Short Palindromic Repeats-CRISPR associated protein) complex with different modes when working individually or cooperating with AcrIF2, which might exclude target DNA binding through different mechanisms. The type I-F Csy complex is a crRNA-guided surveillance complex composed of a crRNA and nine Cas proteins (one Cas8f, one Cas5f, one Cas6f, and six Cas7f), which recruits a nuclease-helicase protein Cas3 for target degradation. CRISPR-Cas immune systems are used by certain prokaryotes and archaea to resist the invasion of foreign nucleic acids such as phages or plasmids. Anti-CRISPRs are small proteins which are the natural inhibitors for CRISPR-Cas systems; encoded on bacterial and archaeal viruses, they allow the virus to evade host CRISPR-Cas systems. The CRISPR-Cas-mediated adaptive immune response can be divided into three steps: the acquisition of spacer derived from invading nucleic acids, crRNA processing, and target degradation. Theoretically, Acr proteins could suppress any step to disrupt the CRISPR-Cas system. Acr proteins are diverse with no common sequence or structural motif which inhibit a wide range of CRISPR-Cas systems with various inhibition mechanisms. CRISPR-Cas systems are divided into two classes (1 and 2) and six types (class 1: types I, III and IV; class 2: types II, V and VI). Class 1 systems utilize RNA-guided complexes consisting of multiple Cas proteins as the effector proteins to recognize and cleave target DNA. Type I CRISPR-Cas systems are the most widespread in nature, and the Cas protein composition of the employed CRISPR ribonucleoprotein (crRNP) complexes differs between seven subtypes (A to F, U). Acr families are named for their type and subtype which are numbered sequentially as they are discovered.
Comment:Multiple copies of AcrIF1 bind to the CRISPR RNA (crRNA)-guided surveillance complex (Csy complex) with different modes when working individually or cooperating with AcrIF2, which might exclude target DNA binding through different mechanisms.
Structure:6B46: Pseudomonas phage AcrIF1 (2 molecules) in complex with Csy3 molecules within the type I-F CRISPR RNA (crRNA)-guided surveillance complex (Csy complex); contacts at 4A. - View structure with Cn3D